1. Field of the Invention
The present invention relates to a four-wheel drive vehicle, specifically to a four-wheel drive vehicle provided with a transversely extended engine and an inter-axle differential mechanism of a planetary gear type for splitting a drive torque between front and rear wheels and an inter-wheel differential mechanism coaxially disposed with the inter-axle differential mechanism on an axle of one of the front and rear wheels which is clear to the engine in a transverse direction of the vehicle.
2. Description of the Prior Art
In a four-wheel drive vehicle in which an engine power is transmitted to drive both front and rear wheels through a torque converter and transmission, some of the vehicles are provided with not also inter-wheel differential mechanism for splitting an engine torque between the front wheels or the rear wheels but also inter-axle mechanism for splitting the engine torque between the front wheels and the rear wheels to thereby eliminate so-called braking effect of the vehicle caused by a rotation speed difference between the front and rear wheels during a cornering operation of the vehicle.
In this type of four-wheel drive vehicle having the transversely arranged engine, the inter-axle differential mechanism is coaxially mounted with one of the inter-wheel differential mechanisms on one of axles of the front and rear wheels which is disposed closer to the engine. Japanese Patent Public Disclosure No. 61-66028, laid open to the public on July 14, 1986, discloses a four-wheel drive vehicle comprises an engine transversely disposed at a front side of the vehicle, an inter-axle differential mechanism coaxially mounted with a front inter-wheel differential mechanisms of a bevel gear type on a front axle. The inter-axle differential mechanism is arranged at one side of the inter-wheel differential mechanism where the inter-wheel mechanism faces to the engine. The four-wheel drive mechanism is also provided with an inter-axle differential restricting device for controlling a differential operation of the inter-axle differential mechanism so as to restrict a differential movement between front and rear axles under a certain condition.
In a power transmitting mechanism for a four-wheel drive vehicle, it is critical that a transfer mechanism constituted by an inter-axle differential mechanism, inter-wheel differential mechanism arranged close to an engine and the like and integrally connected with the engine and transmission is provided as compact as possible.
Meanwhile, there is provided a transfer housing for receiving the transfer mechanism.
The four-wheel drive mechanism disclosed in the Japanese Patent Public Disclosure No. 61-155028 is disadvantageous in that the inter-axle differential restricting device is located outside of the front inter-wheel differential mechanism to cause a housing portion for receiving the front inter-wheel mechanism to increase in size.
Japanese Patent Public Disclosure No. 57-126727 discloses a four-wheel drive mechanism including a trans-axle housing connected with an engine and receiving a clutch and transmission and a transfer housing connected with the trans-axle housing at one side of the trans-axle housing which side is close to the engine. In this arrangement, a joint surface of the trans-axle housing and the transfer housing is aligned with a joint surface of the trans-axle housing with the engine so that the transfer housing projects transversely toward the engine. This limits the transfer housing space for receiving a catalytic converter and the like.